Demon beasts are not puppet beasts; they also need rest.
The demon beasts attacking Zhenyue Immortal City had traveled long distances without proper rest for several days.
The reason they still attacked the Immortal City under such circumstances, besides the high-tier demon beasts wanting to test the city's defensive forces, was also to cull some low-tier demon beasts to reduce the burden on the beast horde's food supply.
By relying on strength and the "Beast King Horn," high-tier demon beasts could intimidate and restrain herbivorous and carnivorous demon beasts from slaughtering each other, but they couldn't stop hungry demon beasts from doing so.
An occurrence of a "Beast Tide" often takes years to conclude fully, so for the high-tier demon beasts, controlling the scale of the "Beast Tide" to prevent massive losses due to food shortages is a test of wisdom.